1. Field of the Invention
The present invention generally relates to an infusion device suited, but not exclusively limited thereto, for the infusion of medical solutions to a patient. More specifically, the present invention relates to a peristaltic infusion pump utilizing the peristaltic action to accomplish a pumping of a fluid medium through a flexible and compressible tubing.
2. Description of the Prior Art
An example of prior art peristaltic pump assemblies is schematically shown in FIGS. 6 to 8 of the accompanying drawings. FIG. 6 is a schematic top plan view of the prior art peristaltic pump assembly; FIG. 7 is a schematic side view as viewed in a direction perpendicular to a drive shaft 3, showing a portion of the housing; and FIG. 8 is a schematic cross-sectional view, on an enlarged scale, taken along the line C--C in FIG. 6.
The illustrated peristaltic pump assembly comprises a housing including at least top and bottom walls 1a and 1b connected together so as to define a cam chamber therebetween. A drive shaft 3 having one end drivingly coupled with any suitable drive motor, for example, a stepper motor, extends rotatably, but axially non-movably through associated annular bearings 2 mounted on those walls 1a and 1b in any known manner. A plurality of round cam plates 4 are situated within the cam chamber between the top and bottom walls 1a and 1b and are rigidly mounted on the drive shaft 3 for rotation together therewith. Generally rectangular finger plates 5 equal in number to the number of the cam plates 4 are also operatively accommodated within the cam chamber, each of said finger plates 5 having an aperture defined therein to accommodate the associated cam plate 4. As will become clear from the subsequent description, each of the finger plates 5 is movable between retracted and projected positions in a direction perpendicular to the drive shaft 3 during the rotation of the drive shaft 3 and, hence, that of the associated cam plate 4.
A stationary back-up plate 6 is positioned parallel to the drive shaft 3 and in the vicinity of the projected position of each finger plate 5 with a flexible and compressible infusion tubing 7 extending therebetween. This infusion tubing 7 has an upper end fluid-connected with a well-known source of infusion solution (not shown) and a lower end fluid-connected with an injection needle or a infusion catheter (not shown) and then to a patient. For the purpose of discussion, a portion of the infusion tubing 7 between a finger tip 5a of one of the finger plates 5 closest to the top wall 1a and a finger tip 5a of another one of the finger plates 5 closest to the bottom wall 1b and along the stationary back-up plate 6 is hereinafter referred to a pumping section of the infusion tubing 7.
As best shown in FIGS. 6 and 8, the round cam plates 4 are eccentrically mounted on the drive shaft 3 along the longitudinal axis of the drive shaft 3 in a manner which will create a peristaltic action by the movement of finger plates 5 as will be described later. With the round cam plates 4 so mounted eccentrically on the drive shaft 3, each round cam plate 4 generally has protruding and retracting lobes opposite to each other with respect to the axis of the drive shaft 3, the protruding lobe representing a maximum radius a.sub.1 radially away from the axis of the drive shaft 3 while the retracting lobe represents a minimum radius a.sub.2 radially away from the axis of the drive shaft 3 as shown in FIG. 8. These cam plates 4 are so eccentrically mounted on the drive shaft 3 for rotation together therewith that the respective protruding lobes will be sequentially displaced an angle of n/360 degree about the axis of the drive shaft 3 from each other in a direction circumferentially of each cam plate 4, wherein n represents the number of the cam plates 4. As illustrated in FIG. 8, eight cam plates 4 are employed and, hence, the respective protruding cam lobes are circumferentially displaced 45 degrees about the axis of the drive shaft 3. In any event, the round cam plates 4 are eccentrically mounted on the drive shaft 3 in a helical pattern along the axis of the drive shaft 3.
Each of the apertures defined in the finger plates 5 and operatively accommodating therein the respective cam plates 4 is so shaped and so sized that, during one complete rotation of the associated cam plate 4 together with the drive shaft 3, the respective finger plate 5 can be driven or slid reciprocally between the projected and retracted position in a linear direction perpendicular to the axis of the drive shaft 3. Therefore, the rotation of the cam plates 4 together with the drive shaft 3 and within the apertures in the associated finger plates 5 causes the respective finger plates 5 to sequentially move between the projected and retracted positions thereby creating a peristaltic action by which the pumping section of the tubing 7 are progressively squeezed by the respective finger tips 5a of the finger plates 5 in cooperation with the stationary back-up plate 6 to accomplish a continuous volumetric displacement of the infusion solution through the pumping section of the infusion tubing 7.
The foregoing example of the prior art peristaltic pump assembly is substantially disclosed in, for example, U.S. Pat. Nos. 4,617,673, issued Oct. 14, 1986; 4,690,673, issued Sep. 1, 1987; and 4,952,124, issued Aug. 28, 1990, and U.S. patent application Ser. No. 07/513,886, filed Apr. 24, 1990 now abandoned.
Briefly speaking, the prior art peristaltic pump assembly of the type referred to above is of a design wherein the finger plates 5 successively driven by the cam plates 4 sequentially squeeze the pumping section of the infusion tubing 7 while producing a zone of occlusion that is progressively moving along said pumping section in a direction conforming to the direction of flow of the infusion solution.
When it comes to a mass production of the peristaltic pump assemblies with a view that the resultant products can be made available at a reduced price, any dimensional deviation among the component parts of identical design and/or shape used in one or more lots of the peristaltic pump assemblies may cause the pump assemblies of the different lots to exhibit a different pumping performance, for example, a different pumping rate. By way of example, the illustrated peristaltic pump assembly employs one or more groups of component parts of identical design and/or shape such as a group of the cam plates 4 and a group of the finger plates 5. If one lot of the cam plates and another lot of the cam plate have a dimensional deviation from each other, not only may the single peristaltic pump assembly exhibit a fluid pumping rate deviating from the design parameter if such single peristaltic pump assembly employs the cam plates selected from these different lots of cam plates, but the peristaltic pump assemblies of one batch may also exhibit a fluid pumping rate varying from that of the peristaltic pump assemblies of a different batch.
Let it be assumed that there are patients who require an equal quantity of the same infusion solution to be injected, the use of the peristaltic pump assemblies of varying pumping performance may result in the injection of the correspondingly varying quantities of the infusion solution into the respective patients and/or in that the quantity of the infusion solution actually injected may vary from that specified by a doctor or an attendant nurse. This is not desirable and should be minimized or substantially eliminated.